1. Field of the Invention
The present invention relates to a linear motor for use in various industrial machinery such as, for example, machine tools, electric component mounting apparatus or semiconductor-related apparatus. Particularly, it relates to a moving-magnet type linear motor which is constructed to take a field system as moving element and an armature as stator.
2. Discussion of the Related Art
As a moving-magnet type linear motor which takes a field magnet as moving element and an armature (coreless coils) as stator, there has been known one which is described in Japanese published utility model application No. 07-30585. This is of the construction that a moving-magnet body is configured by fixedly piercing a through shaft member into a holed column permanent magnet and that the through shaft member is axially slidably carried by bearing members so that the moving-magnet body is axially movable inside coreless coils which are in fixed relation with the bearing members. In this device, a propelling force acting on the moving-magnet body is basically in accordance with Fleming's left-hand rule. (Although Fleming's left-hand rule is applicable to the coreless coils, the propelling force given to the moving-magnet body is generated as a reaction or counter-force of the force acting on the coreless coils because the same are provided stationarily.) Thus, contributed to the propelling force is a normal component of magnetic flux of the permanent magnet provided in the moving-magnet body (i.e., a component normal to the axial direction of the permanent magnet).
As a moving-magnet type linear motor of another kind, there has been known one which is described in Japanese unexamined, published patent application No. 1-270763. This is of the polyphase type that a plurality of coreless coils on a stator side apply a propelling force to magnets on a moving member side. Specifically, the coreless coils arranged in the moving direction are secured to stick-like support members at their opposite ends in a direction normal to the moving direction to constitute an elongated stator assembly. The moving member surrounding the elongated stator assembly is movable along the same, and the magnets attached to each of facing interior surfaces of the moving member are located between the support members securing the opposite ends of the coreless coils, to face one-end surfaces and the other-end surfaces of the coreless coils. Pipe conduits for flowing coolant therethrough are provided inside each of the support members in the moving direction, so that the heat generated by drive current applied to the coreless coils can be removed by circulating coolant through the pipe conduits.
However, in the technology of the aforementioned Japanese published utility model application, the moving-magnet body is configured by the column permanent magnet which surrounds the circumferential surface of the through shaft member, and this gives rise to a drawback that the mass of the moving-magnet body increases to result in a poor responsiveness. Further, in the technology of the aforementioned Japanese unexamined, published patent application, the cross-section of each support member in which the pipe conduit is provided for flowing coolant therethrough is so larger as to make the heat from the coreless coils spread over the whole of each support member, and this gives rise to a drawback that the heat conduction between the coreless coils and the coolant is low in efficiency. In addition, consideration should have been taken into a universal problem that when a metal member moves across magnetic flux, eddy current is generated to decrease the propelling force for the moving member.